Regeneration of olefins from acid solutions



ug- 7, 1951 F. M. ARCHIBALD x-:T AL 2,553,686

REOENERATION OF OLEFINS FROM ACID SOLUTIONS Filed April 15,` 1948 dmmouml lvdmmzmQzOU duk/x3 Francis hldrcbibald U'nceni F'mn'stre'a tions.

Patented ug. 7, 1951 REGENERATIN OF OLEFIN S FROM ACID SOLUTIONS FrancisM. Archibald, Elizabeth, and Vincent F.

Mistretta, Fanwood, N. J., assignors to Standard Oil DevelopmentCompany, a corporation of Delaware Application April 15, 194s, serialNo. 21,174

8 Claims. 1

This invention relates to a p-rocess for the recovery of olenhydrocarbons from strong acid extractsof the corresponding alcohols oracid esters of the respective olens. More particu larly, theinventiondeals with the recovery of the lower molecular weight olefinhydrocarbons, e. g. of the C2 to C6 range Asuch as ethylene, propylene,isobutylene, n-butenes, and the isomeric amylenes, etc., from acidextracts of their corresponding alcohols or acid esters. The desiredolefin recovery is accomplished in this invention by passage of the acidextracts in long thin streams of denite length and cross-sectional areaunder specific conditions of temperature, now rate, and acid strength toassure high yields of the desired olefin in high purity.

The prior art discloses that oleiinic hydrocarbons can be prepared fromthe corresponding alcohols or acid esters by heating their acidsolutions. The control over the reaction indicated by the prior art hasbeen regulation of the temperature, acid strength and alcoholconcentration. Some mention has been made of the concentration ofesteried olefin present in the acid solu- Disclosures of the prior artcan be surnmarized by `stating that the acid solutions are either (l)diluted, (2) maintained at a lower con- `centraton by the presence of anexcess of alco hol during distillation, (3) the distillation of the acidliquor is carried out inthe presence of a salt, (4) acid liquor isheated to polymerize iso C4=. The following patents are representativeof the prior art:V Englehardt et al. 1,770,734; Deansley et al.2,012,785; Snow 2,128,971; and Deansley 2,237,292.

The prior art does not disclose processes for recovery of oleflns'.particularly isobutylene, in high yields from acid extracts containingacid at or closely approaching absorbing strength for the olefin.Neither does it show a process for recovering olen from an acid extractcoincident with increasing the acid strength from somewhat belowabsorbing strength to absorbing strength. The teaching of the prior artthat any suitable means of applying heat quickly to an acid exp tractwill cause regeneration of olefin is only correct when olefin yields ofless than 20% are considered as proper demonstation of the art. It willbe demonstrated in the examples that to maintain yields of olefinabove,5060% it is neeessary to use the process described by thisinvention as contrasted to any process to be devised by implicationsfrom the prior art.

The olen regeneration process as described in this invention diners fromthe processes of the prior art in that: (l) extremely large yields ofolefin, e. g. 8090 weight percent and above, are obtained therefrom, (2)during the recovery process the acid strength is increased from somewhatbelow olefin-absorbing strength up to olefin-absorbing strength, thusrequiring no restoration or reconcentration before being returned to theabsorption system and (3) the purity of the regenerated olen isextremely high, e. g. S65-99% in the case of isobutylene.

In application Serial No. l21,173 filed of even date herewith in thename of Matthew D. Mann,

Jr. and Henry Oi. Mottern, there is described and claimed a process forthe regeneration of olens from acid extracts thereof by decomposition ofthe acid solution by flash vaporization under controlled heat transferconditions whereby the extract is fed to the heat exchange zone in theform of streams of restricted length and cross-sectional area, such, forexample, as would be obtained by passing the extract through thecylindrical tubes of a tube-in-shell type heat exchange.

The novelty of this invention resides in the olen regeneration processwherein the acid extract or acid solution is fed to the decompositionzone in streams which are non-circular in crosssectional area, e. g. astream which is elliptical in cross-sectional area, whereby heattransfer into the vapor producing feed material under ash reactionconditions is enhanced. The improved yields of regenerated olen achievedby employing streams whose cross-sectional area are non-circular, e. g.elliptical-shaped streams such as are obtained by passing the .j'acidextract through a partially flattened tube, are not predictable from theReynolds number since the velocity of flow increases about one hundredfold as the extract passes through the decomposition zone due to theformation of the gas phase.

It is an object, therefore, of this invention to provide an olenrecovery process in which high yields of recovered olefin are obtained.

It is another object of this invention to provide a process for olenrecovery from their acid solutions in which the acid is recovered fromthe regeneration in increased strength.

It is a further object of this invention to provide a process for olefinrecovery in which the purity of the recovered olefin is extremely high.

These and other objects of the invention are accomplished by carryingout the regeneration according to the process which will now be setforth.

The practice of this invention will be described for illustrativepurposes only using so'butylene and its sulfuric acid extracts as thereference materials. The acid extracts are prepared by the methodsdisclosed in the art, namely, acid treatment of a butane-butene fractionfrom petroleum or other sources under controlled conditions oftemperature and pressure using (S-70% H2804. After the acid extract issettled free of the unabsorbed hydrocarbon, it it decanted and is readyfor use in the isobutylene recovery process.

The isobutylene recovery is carried out as follows: Isobutylene acidextract is diluted with Water from absorbing strengths of E50-70% to55-60% acid strength, calculated on a hydrocarbon free basis. Theentrained and dissolved gases are allowed to disengage from the extract.The extract is then passed in long thin heated streams of restrictedlength and non-circular cross-sectional area into uniform contact with aheat exchange surface, preferably e. g. by passage through apartially-flattened tube contained in a tube-in-shell heat exchangerunder carefully controlled flash vaporization conditions, hereinafterdescribed, which causes the isobutylene to regenerate from the acidextract. The isobutylene gas and acid efliuent from the exchanger tubesare carried rapidly into a disengaging vessel where the gas is takenoverhead andthe acid iiows out the bottom through a cooler to areceiving vessel for recycling to the absorption unit. The isobutylenepasses from the disengaging vesselto conventional'scrubbing, compressionand fractionating equipment for purification. The process is thusadapted to continuous operation.

The operation of the exchanger-generator is closely controlled as toacid extract flow rate, temperature, pressure, acid strength, extractsaturation, etc., in order to minimize recovery of potential isobutyleneas polymerA or as alcohol.

OPERATING CONDITIONS The acid extract is fed to the exchanger tube at arate which will maintain the entering liquid linear Velocity at 0.4-2.0ft./sec. for each stream entering the heat exchange surface. Velocitieslower than 0.4 ft./sec. cause polymerization and velocities higher than2.0 ft./sec. cause incomplete regeneration of the olefin. The preferredrange of velocity is influenced partly by the saturation of the extract,viz. the mols olefin/mol acid. When the extract saturation is in therange of 0.2-.8v

the preferred velocity is .4-.8 ft./sec. when the extract saturation is0.84.0, the vpref erred velocity is .6-1.0 ft./sec. When the extractsaturation is above 1.0 the preferred VelocityV is at 1.0-1.2l ft./sec.Y

The regeneration must be carried out at absolute pressures between600-1000 mm. Hg. At pressures below 600 mm. too much of the olen isrecovered as the corresponding alcohol to give a good yield per pass andcan only be converted to olefin by recycling to the process. Atpressures over 850 mm. the yield of isobutylene is reduced throughpolymerization. Only at pressures close to atmospheric can the yield ofolefin be held to a high figure, i. e., above 80 Weight percent.

The temperature of the reaction is measured at the outlet to theexchanger tubes. This temperature is held at a point to indicate theboiling point lof the acid at the desired strength. The

. temperature is a function of the pressure, rate of heat input and thepartial pressure over the acid. The partial pressure is Vinfluenced bythe quantity of olefin regenerated. For example, where temperatures of150 C. may be required to recover the 4 acid at 65% from extracts of 0.5saturation, extracts at 1.0 Vsaturation give sufficient gas to give 65%acidat 135 C. At the preferred rates of flow, the acid strength was heldat 65%.

Although the regeneration to high yield is operable in the range of6'0-7 0% effluent acid strength the preferred range is (S4-66%. Thestrength is sufficient for fast absorption rates and gives lesspolymerization in the exchanger generator. The dilution of the extractfrom the absorber is made to give 55-60% acidl for regeneratingisobutylene. The regeneration of ethylene, propylene or n-butylene iscarried out at higher acid strengths and temperatures.

The length andvdi'ameter of the heated stream of extract must be limitedto maintain a high yield of olen. When a tubular heat exchanger isemployed in the process, these factors can be controlled, of course, bythe length and diameter of the exchanger tubes themselves. The lengthmay preferably vary between 3 ft.'and 10 ft. Tubes shorter than 3 ft. donot give enough surface and heat to insure vcomplete regeneration orrecovery of 'isobutylene developmentof pressures above 5 lbs. inducingexcessive polymerization. The minor diameter of the stream (in the caseof elliptical streams) or the central minor axis of the stream can varybetween le" and 3X1 in length, assuring a flow velocity for a givenextract in the proper velocity range as indicated above.

The following discussion illustrates the effect of operating Variableson the overall process'yields etc. as determined by actual plant runs onthe regeneration of isobutylene from sulfuric acid exf tracts.V

EFFECT oF LENGTH AND DIAMETER or ExTRAoT STREAM lent in performance andwas used in most of the experimental work. The tubel length was variedat 3', 5 and 10' to explore the relation-V ship between the volume ofliquid feed and tube length. Lengthening the tube increased isobutyleneyields at a given feed rate. Linear velocities below 0.3 ft/sec. showlowyields of iso-V butylene for all tube lengths. At 0.4-0.8 ft./sec.,regeneration yields approach a maximum for each tube` length. This isshown in Table I following. Y

Table I EFFECT or FEED RATE oN TUBE LENGTH Ik O. D., Mt I. D. coppertube. Extract saturation=0.5. Outlet temperature=l509 0.]

Y Tube Length Linearr Y Y A Y d l u Y veioeay', 3" 5 10' ft./sec.

Weight Per Cent Iso Cl-(on Recovered Products) Tubes longer than l0 ft.cause Y Table II EFFECT OF TUBE LENGTH ON ISOBUTYLENE REGENERATION B O.D., Ma" I. D. copper tube. Feed ratez ft./sec.

- saturation=0.5.]

Extract WighiPerRCent so 4" @3911 Tubelleneth grated (011 Re coveredPlOd' ucts) Polymer and alcohol formation are relatively constant overthe range of practical feed rates- 13.5% polymer and 1.5% alcohol. Thisis illustrated in Table III:

Table III POLYMER AND ALCOHOL FORMATION [14" 0. D., Ma I. D. X 10 ft.tound Clopper Tube. Extract saturaion=0.5.

Weight Per Cent Isobutylene to Feed (on Recovered Rate, Products)ft./sec.

Polymer t-BuOH The small quantity of alcohol produced is contained in awater layer from the condensed overhead stream in the isobutylenerecovery process. The entire water layer can be recycled to the initialdilution stage for reducing the effective acid strength of the extractto 60%. If a water balance is maintained only make-up Water need beadded to the dilution stage. Polymer composition is similar to thatproduced by current steam stripping regeneration technique. A typicalanalysis of the polymer produced from an extract containing 93 weightper cent isobutylene and 'l weight per cent normal butylene, 52.8%dimer, 22.7% trimer, and 24.5% codimer.

Tube diameters were varied between 1A and 1%" for copper, Nichrome, andtantalum. The

.1/2 O. D. (115" I. D.) tube was the largest diameter tubing used thatgave no isobutylene in the spent acid. Too large a. tube permits slugsof only partly heated extract to be blown through the tube before theolen is adequately liberated. Since the 1A" tubing seemed impracticalfor commercial use, the 1/2" was chosen for study. The data on theeffect of tube diameter of 3 ft. lengths are summarized in Table IV,following. It is apparent that the smaller the diameter. the greater isthe regeneration of isobutylene.

Table IV EFFECT 0F TUBE DIAMETER- [Length=3 ft. Feed rate=0.40.6ft./sec.]'

Weight Per Cent Iso C4* to (on Recovered Products) Tube Inside DiameterRegen.

erated Iso C4- in Isobu- Polymer tBuOH Spent Acid tylene W copper 78.016.1 4. 2l 0 ils steel 60. 9 26. 0 13.1 0 Ms copper 63.0 25.0 12. 0l 0Nlchrome 55.3 8.0 3.0 32. 5 15e tantalum thimble (heated internally) 35.5 27. 5 2. 7 33. 3

EFFECT 0F SHAPE 0F EXTRACT SLREAM DURING REGENERATION Flash regenerationof isobutylene requires a high rate of heat input combined with a shortcontact time. The shape of the surface over which regeneration takesplace has been found to aiect therate of heating and the uniformity ofiiow over that surface with consequent effect on regeneration.` Thisrelationship was demonstrated by altering the shape of the extractstream, i. e. for example, the shape of theexchanger tubes.

A 1/2 tube, iiattened to 1A minimum diam-v eter, showed higher yieldsthan a round tube of similar length. A comparison of 3' and 5' tubelengths in both round and at tubes is shown in Table V. Y

Table V EFFECT oF TUBE SHAPE 0N RE GENERATION [Tube 1ength=3 and 5.Extract saturation=0.5. le round tube vs. li tube iattened to M minimumdiameten] i Weight Per Cent Iso Gi Reg. (am Linear Recovered Products)Velocity, ft./sec.

3 Round 3 Flat 5 Round 5 Flat 0. 2 56. 5 83.0 78. 0 0. 3 63.0 84. 0 78.5 B4. 0 0. 4 63. 5 85. 5 80. 0 B8. 0 0. 6 64. 0 80. 0 80. 0 B7. 0

Feed rate appears critical for the flattened tubes for a given length.

The effect of flattening a 1/2 x 5 tube on regeneration was equal toincreasing the length of the cylindrical tube to 10 feet. Considerablyhigher yields were obtained for the flattened tube in a feed rate rangeof 0.30.6.

Table VI EFFECT 0F TUBE SHAPE 0N REGENERATION Filler bars were tried inshort length tubes larger than 1A". In order to test this, 1A", 1%, and11g" ller bars were inserted within a 1/2 x 3' tantalum tube. An annularspace above Weight Per Cent lso Cl-'Ren gnenxrated) (onLvRecoverel i erro uc s at inear e Annuler l 015%' space (ft/sec.) of

A, Inchesy lInches .l Y,

. $4 le 65.0 62.5 '1% lit 60. 0 74.0 78. 5 Zia e2 69.6 80.0 88.5

Adiierent type of vannular space was tested on a 'l1/2" '0. D; x 28"tantalum thimble inserted in a c'arbate lined Yspool piece leaving aV1/4 inone 'case and 1/2 annular space in another case. In both cases lowisobutylene yields'were noted, probably due to poor distribution on 'thethimble. The following table illustratesthe decrease in yield 'withincreasing feed rates. Regeneration 'of the extract was incomplete inall cases.

Table-VIII EFFECT OF ANNULAR SPACE USING A TANTALUM THIMBLE [Heatedinternally] Weight Per Cent Iso Cl'- regenerated (on Recovered Prod-Linear Velocity, ucts) ft./scc.

%Anuular fx/Annuler Space Space summarizing the data on the effect of'tube shape or surface phenomena -onregene'rationlin -heat exchangeequipment, it is shown that aiattened tube gives the highest isobutyleneyield iorva ygiven length. The limiting4 capacity for `an Yexchanger of-al givensurface area appears about the same with round o'r yflat tubes.Table IX summarizes data on the effect of tube shape on regeneration.

Table IX EFFECT OF`TU`BE SHAPE ON REGENERATION Weight Per Cent Iso C4regenerated (on Recovered Y Products) at Linear Vel.

Tube (ft/sec.) of

Round copper tube Zic I. D. x 36". 56. 5 63. 0 64.0 Flattened to 1A(same as above) 83.0 83.5 78. 5 I. D. X BGM-H filler bai- 57.0 74. 078.5

1% O. D. X 28 tantalum'thimble (heated'internally) l .Y 55. 7 41.4 v.35. 3

The extract streams being subjected to heat exchanger-should preferablyvflow in .a zdescer'ioling stream. For example, when exchanger tubes areemployed they-should be placed in a vertical position to insure evendistribution'of extract through each tube. A poolof extract aboveV thetube bundles would provide uniform distribution through orices into eachtube. Carbate vis recommended as a material for the distribution plateand should be-th-ick enough to thermally insulate the extract above theorices. When the extract streams were allowed to yiiow in a lateraldirection poor yields of regenerated olefin resulted. When the extractstream is subjected to heat exchange in an up-ow direction, extremelypoor yields of regeneratedA olen resulted. The poor yields in theseinstances are due, undoubtedly, to two factors, namely, the pressurerequired to promote proper flow of the extract stream, and secondly, thecollection of acid which occurs under conditions of lateral flow andup-flow. The pressure employed is conducive to polymerization of theolen, likewise, contact with acid at the temperature employed isconducive to polymerization which, of course, detracts from the yield ofdesired olefin.

EFFECTv oF. ExTRAoT SATURATION The satu-rationfof theext-racts employedin the olefin regeneration process is? preferably ybetween 0.5 and 1.5.Experiments were carried out employing saturations in the above regions.Extracts of 1.0 saturation were found to give on regeneration, yields of83% at 0.6 ft./sec. feed rate. On increasing the extract saturation to1.5, it was found necessary to increase the feed velocity to to 1.1ft./sec. to reach an 85% yield. The higher feed velocities werenot-'necessary to secure good yields at the 0.5 saturation. At thehigher extract saturation less steam pressure was necessary to maintaina spent acid strength of 65% H2SO4 indicating a greater steam eiiiciencyfor regeneration. Table X summarizes data on'the effect ofextract'saturation at various feed velocities on isoloutyleneregeneration.

Table X EFFECT OF EXTRACT SATURATON De O. D., Mo l. D. x l0' coppertube] l WeightPerCent Isobutylenc` y (on fRec. Prod.) at Linear 1 PerCent Extract Vel. of-

HzSOl in Saturation Spent p. s. 1. g. Acid 0.4 0.6 1.1

0 4-0. 5 84 5 85. 0 80-120 67. 0 1.06 85 0 83.0 l. 82-96 Y67.0 l 3-1.4v68 0 74.0 '85.0 V638-109 '65.2

equipment heatloss.

yl-llulrr REQUIREMENTS Heatrequirements for regeneration and acidconcentration were determined by measuring `the total condensed steamfrom the heat exchanger. A -blan-k run was Vmade for each experin'ieritAlfor The results showed that 30D-375B. t( u.V per'flb. 60%v acid extractwould fbe required over the rangevo'f"0.5l.5 saturation.

This includes heat required Vto raisewthe acid from' 15 C. v-to 150 C.,to r'egeneratethe isobutylene :and to increase the 'acid` strength fromA60% to 65%.

ISOBUTYLENE PURITY Isobutylene purity is .in a range .o'iY 964.99%.

An extract feed containing 91.5% isobutylene and ,8.5% n-,butene vyieldsAisobutylene of 98,9% purity (by VHC'l method). The normal olefins 9 areusually found as codimer in the polymer produced.

REAcToR PRESSURE Reactor pressure was maintained below 2.0 p. s. i. g.Previous laboratory work above this pressure showed that excessivepolymerization occurred. Low pressure on the system was obtained byincreasing the size of the outlet piping from the acid settler to reduceback-pressure.

FEED ExTRAcT ACID STRENGTH Feed extract acid strength of close to 60weight percent H2SO4 (hydrocarbon free basis) was used in theregeneration of isobutylene. Previous laboratory studies indicated that58-60 weight per cent feed acid (after dilution) gave higher yields andincreased product purity.

SPENT ACID STRENGTH Spent acid strength held at 65% by controllingoutlet temperatures. No isobutylene was present in the spent acid atoptimum operating conditions. No further acid concentration of the spentacid is required for absorption. The spent acid is cooled and recycleddirectly. The strength of the spent acid was easily held during a widerange of operating conditions, i. e., feed rates 0.1-1.1 ft./sec.,extract saturations of 0.5-1.5 and feed acid strength of 58-60%.

A very important part of the process for regenerating olens by thetechnique described is that the acid can be recovered in condition forrecycling directly to the absorption step. The acid as recoveredcontains only traces of separable carbonaceous and polymeric hydrocarbonmaterial and these traces are removed by adequate settling facilities.Other processes requiring dilution and reconcentration steps' oftencause the inclusion of such materials in the acid of absorption strengthand result in emulsion formation in the extraction step or foaming inthe regeneration step. Acids recovered at recycling strength from theprocess described are clean enough to avoid such occurrences.

OUTLET TEMPERATURES Outlet temperatures were adjusted to maintain aspent acid strength of 65% H2504. Extracts of 0.5 saturation were heldat 150 C., 1.0 saturated at 145 C. and 1.5 extracts at 135 C.Temperatures were controlled by varying steam pressure on the shell sideof the exchanger. The temperature employed must be such thatpolymerization and other secondary reactions are avoided. The latterundesirable elects are presented by properly correlating the temperaturewith the contact time.

TUBE METAL Tantalum metal is recommended for the exchanger tubeconstruction. Tantalum was tested by passing 65% H2SO4 through a tube ata rate of 10 gallons/hour (0.6 ft./sec.) at 150 C. for 190 hours. Noindication of corrosion or erosion was noted in this service. Theexperimental tube showed no signs of distortion under 125# externalsteam pressure.

The drawing represents a ow diagram showing an elevational view oftypical plant apparatus employed in carrying out the invention.

Referring to the drawing the invention will be described with respect tothe regeneration of isobutylene from acid extract although the inventionis by no means limited to this particular oleiin. Numeral 1 represents adegassing drum to which a 60-70% sulfuric acid extract is led via line2. The extract consists of a solution of C4 hydrocarbons obtained bysulfuric acid treatment of a butane-butene fraction from petroleum orother sources under controlled conditions of temperature and pressureemploying 60-70 weight per cent sulfuric acid. This extract is dilutedwith water entering through line 3 until it reaches an acid strength of55-60%. In the degassing drum entrained and less reactive, unabsorbed C4hydrocarbons are removed via line 4. The temperature employed in thedegassing drum is a temperature below that at which polymerization ofthe isobutylene or copolymerization of isobutyiene-butene occurs. Theextract is pumped from degassing drum via line 5 to regenerator E. Inthe drawing the regeneration zone is illustrated as a verticaltube-in-shell heat exchanger, the tubes of which have been partiallyflattened so as to be elliptical in cross-sectional area. Numeral 'lrepresents the exchanger tubes which may vary in length, preferablybetween 3 and 10 feet as previously described and 1A" to 1%" preferably1/2 in diameter. The extract is rapidly heated by passage through thetubes at a pressure below 2.0 p. s. i. g. and linear velocity of 0.4 to1.2 ft./sec. The temperature during this passage is maintained atapproximately the boiling point of the acid by circulation of steam orother iluid in indirect heat exchange with the extract by entrancethrough line 8 and exit through line 5. For the regeneration ofisobutylene and other tertiary olens such as tertiary amylene, atemperature in the range of 13D-160 C., preferably 140-155" C., isemployed. Straight-chain olens of the C2 to Ce range require higher acidstrengths for absorption. Consequently, to maintain an acid of absorbingstrength at the outlet of the heating zone higher temperatures arerequired, e. g. C. to 295 C., preferably 290 C. to 295 C.` duringethylene regeneration, 165 C. to 278 C. during propylene regeneration,and 180 C. to 255 C. during n-Ci-Cs olefin regeneration.

Under these `conditions the aqueous acid extract is decomposed to yielda gaseous mixture comprising isobutylene vapor, water vapor, alcohol andpolymer vapor and liquid sulfuric acid. The gaseous mixture and acideiiluent from the exchanger tubes are carried rapidly through linel0'into a disengaging drum Il. It is essential that the evolved olen beremoved from the hot acid as quickly as possible to prevent excessivepolymerization of the olefin. In this drum the gas is separated from theacid and removed from drum Il via line I3. The acid settles and isremoved via line l2. This acid becomes concentrated during passagethrough the regenerator and is restored to 60-7 0% concentration inwhich condition it is ready for re-use in the absorption of theCi-hydrocarbon stream. The gas emerging from line I3 passes to a partialcondenser Ill in which hydrocarbon polymers, alcohol and Water arecondensed and removed from the system via line l5. Isobutylene isWithdrawn through line I6 and countercurrently scrubbed in vessel I1 bydilute aqueous caustic for removal of traces of acid. The acid-freeisobutylene .is removed from vessel I1 via line I8. It is thenWater-scrubbed, condensed and stored.

It will be apparent that a system has been described for the rapiduniform heating of the extract with low contact time by passing it infinelydivided streams at high velocity in contact with heat exchangesurfaces whereby the extract is decomposed and the isobutylene evolvedthere- Al1 from. Although Athe flash evaporation process prefer-ablycarri-ed .out employing the heat leX changeregenerator described othermeans canV be employed for providing a plurality .of long unit l2 inlength .upfto 10 feet and between 1A." and 9A", preferably 1/2 in thesmaller diameter. `In lthis manner the distance of any extract particlefrom any heating medium or heat exchange surface paths of extract nowrelativelythin in at least -5 will be kept at a required maximum duringpasone transverse dimension so that all the extract sage of the extractthrough the heating medium liquid is kept Within a certain specifieddistance or heat exchange surface. at all times from the heat exchangesurface.

Another successful lmethod employs a system ISOBUIYLENE REGENEATION.whereby the extract is Vspraiyed Via.ai Shower Experimental runs werecarried out to demon-'- spray, or series of sprays, countercurrent to astrate the improvement obtained by the use of uniform blanko; of Steammaintained ai; a tomflattened tubes for the regeneration ofisobutylperature hotter than the boiling point of the exene fromVsulfuric acid solutions. In the runs tragt, e above 150 C foi` 65%H2504, Steam listed the experiments were carried out under pressures ofabove about 54 pounds gouge are rol5 conditions falling within thefollowing ranges: quired, In this operation the olenn becomes (11S- 1.Linear velocity of' stream: 0.4 to 1.2 ft./'sec. ega'ged from thedeco-mpsed extract artdfpalS-SS 2. Outlet temperatures: 130 to 160 C.,usually with .the steam `overlfiead from the settling acid. 1404555 C-The gas 1s then separated, scrubbed and con- 3 Extract saturation. 0 4to 1 4. dens'ed as descrlbet? above' d t th h t 2.0 4. Regeneratorpressure: 0.9 to 2.0 p. s. i. g.. Y In the regenera 1011 Zone con' 1wpsroug Qu 5. Weight per cent H2SO4 in absorption stage:

are to be closely .controlled to atta1n best opera- 63 65% non' ProperHOW of the extract 1s. nessary.' so 6. Weight per cent H2SO4 in extract(hyd. free that all parts of it receive Substantially identioal 0 v d. th t t t .t Th. basis) after dilution 58. 60.7%. and immeia eeaV rea men.V1s 1s .accom- 25 7. Weight per cent H2SO4 in spent acid (hyd. pl-ishedby proper association of the heating `inefree basis) 65 68 0% dium orheat transfer elements with the respec- 8 Emmet streams produced bypassage through tive extract paths. Every part ofthe extract tubes asindicated. stream during its passage through the regeneration zone liessuiciently close to the heating me- Table XIV is a summary of datashowing the dum 01* transfer element to insure uniform- IllOleadvantageous IBSUIS O'baIIled employing ity 0f 'Gemlleature throughoutthe extract during a iiattened stream of extract 1n the regenerationits. brief passage through the regeneration zone. DI'O'CGSS. Such aStream is typied byrastream tube-111611311 heat exchanger equipment isWhlCl'l iS ellipSOldal in Shape. Il'l thelunstabllpreferred for theprocess of this invention belated in Table Ii' such a stream wasobtained .by causet-he-design and arrangement of the tubes passing theextract through a 1/2 .diameter Within the shell is such that the tubesseem to round copper tube which was flattened to a lo" divide the bodyof extract entering the header minimum diameter. Using such a tubev of5" thereof into a pluralityof longitudinal streams length, equivalentorbetter results were .achieved whose greatest length is parallel to thedirection 40 than those obtained With the 1/2" diameter round oiextractflow, thus offering maximum resistance tube 0f l0 ft.`length. Even at 3ft. length the to lateral now. The dimensions of the longitudiflattenedtube produced yields in all cases be,-

nal streams should preferably be 3 or more feet tween 82.2% and 84.3%.

Table XI isoBU'rYLENE REGENERATION FROM A0113 EXTRACT TUBULAR FLASHHEATER .Weight Per Cent Conversions, Weight Per Gent Conversions, TotalMaterial Balances, Weight Per Cent on al lsoCr Recovcred Olen RecoveredCharge Run No. T t 1 S Y isocisoo-t is ori a 'r mi t-B 0H 9C' T0191 BegPolyineg kt-ij3uQH0 (gigi Polgfmer as llen alsglloeln Olefui ISOC* mso*HO w Y A pix 51.1111011119 Cooper 111119V nested sufra-cwest?. sq. it.

77-.7l 21,0 1.a,A 73.6 23.8 1.3 1.3 100.1 100.1.` V99.1 .94. 77.. 9 20.12. o 7 3, 5 23.1 1. 9 1. 4 99. 4 9s. 1 99. 7- '94; s 79.7 17.7 2e 76.520.0 2.5 1.0 i 101.5 101.6 102.5 90.7

it O D., 7As `I. D. x-'Y Round Copper Tube Heated-Surface=0,30;sq. it.

07.7 28.2 4.1 62.3 31.5 'as V2.4 Y 05.6 95.6; 95.5 91.3 52.6 22.5 13.963.6 22.5 13.9. 99.8 95.9v 100.0 97.2 es. 5 25.3 10. 2 es. 1 2s. 7 10. 20 99. 0 99. 0 100.0 102. 0

``1,2 Round Copper TubeFlattened to lfi Minimum Diameter x 5" HeatedSurface=0-563 sq. ft. Y

ss. 7 s. 9 2. 4 se. 7 10. e 2. 4 0. 3 105. 0 105. o 95. 0 99.2 84.9`12.5 2.6 82.3 14.0 2.5 1.2 101.2 101.2` 102.5 104.0 90. 2 7. 0 2. s ss.4 s. 4 2. s 0.4 102. s 102. 7 99. 1 9s. 1

l. Round*Copper'iiibeittd tno 1,4," Minimuru. Diameter): 3' Heatedsurfaee=0s40 sq1 ft.

82.3 15.1 2.5 80.3 15,5 2.5V 1.7 100.0 100.0 :9l 97.4 24.24 11.4 4.381.9 12.2 4.1 1.9 100. 0 100.0 101.0- 95.4 94.1 13.3 2.0 78.2 its 2.41.9 99.9 99.9 97.9 100.5 82.2 14.8 3.0, 70.3 20.3 2.9 0.5 100.9 100.999. e 101.5 82.3 14.0 3.7y 79.9 15:5 3.5 2.1 10110 100.0 100.1 97:7

V TERTIARY AMYLENE REGENERATION Two runs were carried out on theregeneration of tertiary amylene from acid extra-cts obtained 4bysulfuric acid absorption of a Cs-renery hydrocarbon stream. In thepreparation of the Cri-extract, sulfuric acid of about 70% strength wasemployed in the absorption operation. This acid, is of course, a littlehigher than that used in the preparation of the C4-extract. The runsWere carried out in the exchanger-generator apparatus as previouslydescribed employing a flattened tube of 1/2 minimum diameter coppertubes of ft. length. Operating conditions and results obtained aresummarized in the following table Table XII Run Non l 2 lExtract FeedRate, liters/minute Feed Extract Acid Strength (Diluted from 70% to 60%)Extract Saturator Regenerator Outlet Temp., O Spent Acid StrengthHydrocarbon Content Spent Ac1d Product Analysis Weight Per Cent'trace-tar 2 .4 4. 4 8.7 5.3 Per Cent Regen. based on Analy of Product91. 3

strength. For example, when regenerating ethylene from its sulfuric acidextract it is recommended that the extract be diluted no lower thanabout 85% acid strength; -propylene not below about 65% acid strength;n-butenes not more than 60% acid strength; tertiary amylene andisobutylene not below about 55%. These dilutions are recommended forpractical yields of olefin, i. e., 70 weight per cent and above. Whenacid dilutions below these gures are employed olen yield is Ysacriced toalcohol production which would, of course, be recycled to theregenerator feed. Sometimes under these conditions ethers form,particularly if pressure develops in the regenerator. motes loss ofolefin yields.

Phosphoric acid, benzenesulfonic acid or salts yielding such acids maybe employed in place of the sulfuric acid. Mixtures of such acids mayalso be employed. In general polybasic mineral acids or polybasicmineral acid-acting substances may be employed for the preparation ofthe extract feed to the regenerator.

It will be apparent that the process of this invention is applicable tothe evaporation of a vapor producing feed by submitting the feed inllinely divided continuous streams of restricted length andcross-sectional area to constant and uniform heat exchange (direct orindirect) under controlled rates of flow, temperature etc. This isaccomplished by providing preferably a plurality of long unit paths ofow of restricted cross-sectional area and relatively narrow in at leastone transverse dimension through the path wherein the variation inlength of paths travelled This, of course, pro- 14 by diierent portionsof the liquid flowing through the path is small. It will be seen,therefore, that the shape of the non-circular cross-sectional area ofthe stream passing through the regenerator is immaterial as long as anyparticle thereof is kept within the maximum distance tolerated from theheating surface or medium. The non-circular area may be square,rectangular, cross-rectangular, triangular, trapezoidal, polygonal, butpreferably elliptical. However, according t0 the terms of the inventionat least one diameter or central minor axis of the non-circularcross-sectional area must be 1A" to en" in length for an unobstructedstream (i. e. as previously explained the diameter may be increased if afiller bar is employed). Thus, the greatest distance of any particlefrom a heating surface or a heating medium will be M3 to In this mannerthe proper amount of heat is applied to the liquid stream,

uniformly, at the proper time and for the proper duration. Thiscorrelation of conditions is conducive to the high yields of regeneratedolen.

Having described the invention in a manner so that it may be practicedby those skilled in the art, what is claimed is:

l. A process for the regeneration of a monoolen containing 2 to 6 carbonatoms' per molecule from an acid extract thereof which comprisescontinuously passing the liquid extract downwardly at, a linear velocityof 0.4 to 2.0 ft./sec. into one end of an externally heatednon-cylindrical decomposition zone of 3 to 10 feet in length and 1A to3A in central minor axis, maintaining the extract at a substantiallyuniform temperature between C. and 295 C. during passage through thedecomposition zone whereby the acid extract is decomposed tosubstantially a mixture comprising mono-olefin vapor, water vaporv andliquid acid, continuously passing the total extract decompositionproducts from the other end of the decomposition zone into a disengagingzone and rapidly separating and removing said vapors from the liquidacid in the disengaging zone,

2. A process according to claim 1 in which the cross-sectional area ofthe stream is elliptical.

3. A process for the regeneration of a monooleiin containing 2 to 6carbon atoms per molecule from an acid extract thereof which comprisescontinuously passing the liquid extract downwardly at a linear velocityof 0,4 to 2.0 ft./sec. into one end of an externally heated ellipticaldecomposition zone of 3 to l0 feet in length and 1A, to "A" in innerminor diameter, maintaining the extract at a substantially uniformtemperature between 130 C. to 295 C. during passage through thedecomposition zone whereby the extract is decomposed to substantially amixture comprising mono-olefin vapor, water vapor and liquid acid,continuously passing the total extract decomposition products from theother end of the decomposition zone into a disengaging zone, rapidlyseparating and removing said vapors from the liquid acid in thedisengaging zone, and recovering mono-olen from said vapors.

4. A process according to claim 3 in which the extract is fed in aplurality of streams to a plurality of decomposition zones.

5. A process for the regeneration of a tertiary mono-olefin containing 4to 6 carbon atoms per molecule from a sulfuric acid extract thereofwhich comprises continuously passing the liquid extract downwardly at alinear velocity of 0.4 to 2.0 ft./sec. into one end of an externallyheated elliptical decomposition zone cf 3 to 10 feet in length and M1"to 3A" in inner minor diameter,

-aseaee maintaining the extract at a substantiallyunif form temperaturebetween 130 C. and 160 C. during passage through the decomposition zonewhereby the extract is decomposed to substantially a mixture comprisingtertiary mono-olefin vaporwater vapor and sulfuric acid,.con.tinuousl.ypassing the total extract decomposition products from the other end ofthe decompositionzone into a. disengaging zone, rapidly separating andremoving. said vapors from the sulfuric acid in the disengaging zone,and recovering tertiary monoolefin from said vapors.

6L A process for the regeneration of isobutylene fromA a sulfuric acidextract thereof containing 60--70 weight percent sulfuric acid whichcomprises diluting the extract with water until it contains 55-60 weightpercent acid, continuously passing. the diluted extract downwardly at alinearvelocity of 0.4 to 1.2 ft./sec. into-one end of an externallyheated elliptical decomposition zone ofA 3 V to 10 feet in length and1/4 to 3A" in inner minor diameter, maintaining the extract at asubstantially uniform temperature between 140 C. and 155 C. duringpassage through the decomposition zone whereby the extract is decomposedto substantially a mixture comprising isobutylene vapor, water vaporandliquid sulfuric acid of 60-70 weight percent strength, continuouslypassing the total extract decomposition products fromv the other end ofthe decomposition zone into Ya disengag-ing zone, rapidly separatingandremoving said vapors from the liquid acid in the disengaging zone,and recoveringr isobutylene from said vapors.

Y 7. A process for the regeneration of propylene from a sulfuric acidextract thereof containing Z0-92 weight percent sulfuric acid whichcomprisesdiluting theextract-with water until it contains. 65-'70 weightpercent acid, continuously passing the dilutedY extract downwardlyat alinear velocity of 0.4 to 1.2 ft./ sec. into one end of an externallyheated elliptical decomposition zone of 3 to 10 feet in length and 1A."to 3A." in inner minor diameter, maintaining the extract at asubstantially uniform temperature between C. and 278 C. during passagethrough the decomposition zone wherebythe extract is depassing thediluted' extract downwardly at aV linear velocity of 0.4 to 1.2 ft./sec.into one end of an externally heated elliptical decomposition zone of 3to 10 feet in length and 1/4." to 3A. in inner minor diameter,maintaining the extract at a substantially uniform temperature between290 C. to 295 C. during passage through the'de- Acomposition zonewhereby the extract is decomposed `to substantially a` mixturecomprising ethylene vapor, water vapor and liquid sulfuric acid of 93-98weight percent strength, continu'- ously passing the total extractdecomposition products from the other end of the decomposition zoneintoV a disengagingzone', rapidlyseparating and removing saidY vaporsfrom the liquid acid in the disengaging zone, and recovering ethylenefrom said vapors.

' FRANCIS M. ARCHIBALD.

VINCENT F. MISTRETTA.

REFERENCES CITED The following references are of record inthe le of thispatent:

UNITED STATES PATENTS Number Name Date A 2,142,937 Deane'sly et al Jan.3, 1939 FOREIGN PATENTS Number Country Date'- 343^,60'0 Great BritainFeb. 26, 1931 5233894;l Great Britain- July 25, 1940

1. A PROCESS FOR THE REGENERATION OF A MONOOLEFIN CONTAINING 2 TO 6CARBON ATOMS PER MOLECULE FROM AN ACID EXTRACT THEREOF WHICH COMPRISESCONTINUOUSLY PASSING THE LIQUID EXTRACT DOWNWARDLY AT A LINEAR VELOCITYOF 0.4 TO 2.0 FT./SEC. INTO ONE END OF AN EXTERNALLY HEATEDNON-CYLINDRICAL DECOMPOSITION ZONE OF 3 TO 10 FEET IN LENGTH AND 1/4''''TO 3/4'''' IN CENTRAL MINOR AXIS, MAINTAINING THE EXACT AT ASUBSTANTIALLY UNIFORM TEMPERATURE BETWEEN 130* C. AND 295* C. DURINGPASSAGE THROUGH THE DECOMPOSITION ZONE WHEREBY THE ACID EXTRACT ISDECOMPOSED TO SUBSTANTIALLY A MIXTURE COMPRISING MONO-OLEFIN VAPOR,WATER VAPOR AND LIQUID ACID, CONTINUOUSLY PASSING THE TOTAL EXTRACTDECOMPOSITION PRODUCTS FROM THE OTHER END OF THE DECOMPOSITION ZONE INTOA DISENGAGING ZONE AND RAPIDLY SEPARATING AND REMOVING SAID VAPORS FROMTHE LIQUID ACID IN THE DISENGAGING ZONE.